1. Technical Field of the Invention
The present invention relates to electronic circuits for generating random electromagnetic noise; more particularly to integrated circuits and devices that produce broadband electromagnetic noise output for testing, calibration, and other purposes.
2. Background Art
As is well known in the art, electrical noise is an inherent factor in electronic designs. The noise is generated by the random vibrations of conducting electrons and holes in the material. The existence of noise is primarily due to the fact that electrical charge is not continuous, but consists of discrete amounts of electric charge. Since noise is a random event, the instantaneous value of the waveform cannot be predicted at any time, but a gaussian distribution or average value can be computed.
In receivers, the amount of noise generated in a circuit determines the upper and lower limits of an input signal that can be carried without severe distortion. By connecting a noise source to a circuit and measuring the input and output noise levels, the amount of noise generated in the circuit can be determined and represented by commonly-used parameters such as noise figure, Y-factor, noise factor, or Signal-to-Noise Ratio.
Conventional noise generating devices are typically large and expensive devices that must be externally connected to the host device under test in order to make any sort of measurement.
Noise diodes are available, but these components generally do not have predictable and precise output power levels, and are specified without a tolerance level. They also typically do not contain a matched circuit on the output, and the matching network must be incorporated into the host device design.
Geissler's U.S. Pat. No. 3,600,703, Aug. 17, 1971 is a pioneer patent in the operation of diodes in the breakdown region for generating useful noise, and remains an instructive disclosure on the subject.
Solitron U.S. Pat. No. 3,967,187 is a noise diode with a current limiting design. The current limiting is accomplished by using a field effect transistor or FET. The operational characteristics of the FET serve to limit the supply current to the noise diode.
Solitron U.S. Pat. No. 3,675,148 is a noise diode with temperature stability and a matched network connected to the built-in amplifier. The matching is accomplished through the feedback circuitry of the amplifier.
Noise modules have been recently introduced to the market, but these lack close tolerance and precision in the output power levels, and are therefore typically not specified with a tolerance unit. These units are not well matched, and are not repeatable from unit-to-unit, due to the inherent difficulties of dealing with noise, and the limitations of current production methodologies. Noise modules are not fabricated as integrated circuits and not packaged as surface mount components.